Brainstorming a new science fiction piece about aliens witnessing the KT extinction event from space. What I've read thus far shows that, depending on which asteroid you're sitting on, the distance between us and them is about 2-3 Astronomical Units, but that can change depending on either the planet's or the asteroid's revolution around the Sun. Since the technology level is not exactly comparable to ours, I'm just trying to figure out when the Earth would be closest, and therefore, prime for observation from a post on, say, an asteroid very close to Mars. Also trying to figure out how to make some aliens capable to surviving in the belt yet remain undetected (whole point is that we're being watched without knowing). Hope the question makes sense.